Support event monitoring

[jean-airoldie]

Support the zmq_socket_monitored_versioned API to retrieve events for sockets.

My inital idea is to create a unique monitor_addr for each socket. Then we would call zmq_monitor_versioned with this addr to create a ZMQ_PUB monitor socket. The we could create a SocketMonitor which would leverage a ZMQ_SUB and subscribe to the appropriate events. It would then unpack the data into a SocketEvent enum and feed it to a user provided closure. If there is no significant overhead, we should enable that by default.

We could use the same API to create a event logger.

This is required to fix #19.

[jean-airoldie]

From my benchmarks creating a socket monitor that listens to all events has no performance impact.

[jean-airoldie]

It makes sense since:

• The only potential overhead is the send calls on the PUB socket
• Such calls happen very rarely (i.e. when connecting or disconnecting)

[jean-airoldie]

Closed by c6024c47d8e930bafd84876a3f881c1a6e29be7f

[jean-airoldie]

Nevermind the commit was reverted. Created a branch that supports monitoring experimentally.

[jean-airoldie]

I'm really unsure if I like socket monitoring tbh. Can't think of any real use case.